Context: Acute ST-segment elevation myocardial infarction (STEMI) is a leading cause of morbidity and mortality. In experimental models of MI, erythropoietin reduces infarct size and improves left ventricular (LV) function. Objective: To evaluate the safety and efficacy of a single intravenous bolus of epoetin alfa in patients with STEMI. Design, Setting, and Patients: A prospective, randomized, double-blind, placebocontrolled trial with a dose-escalation safety phase and a single dose (60 000 U of epoetin alfa) efficacy phase; the Reduction of Infarct Expansion and Ventricular Remodeling With Erythropoietin After Large Myocardial Infarction (REVEAL) trial was conducted at 28 US sites between October 2006 and February 2010, and included 222 patients with STEMI who underwent successful percutaneous coronary intervention (PCI) as a primary or rescue reperfusion strategy. Intervention: Participants were randomly assigned to treatment with intravenous epoetin alfa or matching saline placebo administered within 4 hours of reperfusion. Main Outcome Measure: Infarct size, expressed as percentage of LV mass, assessed by cardiac magnetic resonance (CMR) imaging performed 2 to 6 days after study medication administration (first CMR) and again 122 weeks later (second CMR). Results In the efficacy cohort, the infarct size did not differ between groups on either the first CMR scan (n=136; 15.8% LV mass 95% confidence interval CI, 13.3- 18.2% LV mass for the epoetin alfa group vs 15.0% LV mass 95% CI, 12.6-17.3% LV mass for the placebo group; P=.67) or on the second CMR scan (n=124; 10.6% LV mass 95% CI, 8.4-12.8% LV mass vs 10.4% LV mass 95% CI, 8.5-12.3% LV mass, respectively; P=.89). In a prespecified analysis of patients aged 70 years or older (n=21), the mean infarct size within the first week (first CMR) was larger in the epoetin alfa group (19.9% LV mass; 95% CI, 14.0-25.7% LV mass) than in the placebo group (11.7% LV mass; 95% CI, 7.2-16.1% LV mass) (P=.03). In the safety cohort, of the 125 patients who received epoetin alfa, the composite outcome of death, MI, stroke, or stent thrombosis occurred in 5 (4.0%; 95% CI, 1.31%-9.09%) but in none of the 97 who received placebo (P=.04). Conclusions: In patients withSTEMIwhohad successful reperfusion with primary or rescue PCI, a single intravenous bolus of epoetin alfa within 4 hours of PCI did not reduce infarct size and was associated with higher rates of adverse cardiovascular events. Subgroup analyses raised concerns about an increase in infarct size among older patients. In a follow-up study, we aimed to determine the feasibility of centrally analyzing EPCs levels to assess the relationship between EPC levels, and EPO administration and infarct size. Methods: Mononuclear cells (MNCs) were locally cryopreserved for central processing from samples obtained prior to rescue or primary percutaneous coronary intervention, as well as at 24 h and 48C72 h postintervention, and analyzed for cells expressing CD133, CD34, and aldehyde dehydrogenase activity. Results: Sampling of EPCs was attempted in 163 of 222 enrolled patients. At least one analyzable sample was obtained in 125 patients, and all three time points were available in 83 patients. There were no statistically significant differences in EPC numbers over time or in the absolute EPC levels between EPO- and placebo-treated patients. There was a trend toward a greater increase in EPC levels from 24 h postintervention to 48C72 h postintervention in patients receiving 30 000 U of EPO ( = 0.11 (placebo) vs 0.092 (EPO), p=0.05). EPC numbers at baseline were inversely related to infarct size (p=0.006, r=-0.39). Conclusions: Local whole cell cryopreservation and central EPC analysis is possible. High-dose (30 000 U) EPO may mobilize EPCs at 48C72 h. Baseline EPC levels are inversely associated with infarct size, suggesting that acute EPC mobilization may be a viable strategy to minimize acute injury. Erythropoietin (EPO) was hypothesized to mitigate reperfusion injury, in part via mobilization of endothelial progenitor cells (EPCs). The REVEAL trial found no reduction in infarct size with a single dose of EPO (60,000 U) in patients with ST-segment elevation myocardial infarction. In a substudy, we aimed to determine the feasibility of cryopreserving and centrally analyzing EPC levels to assess the relationship between EPC numbers, EPO administration, and infarct size. As a prespecified substudy, mononuclear cells were locally cryopreserved before as well as 24 and 48C72 h after primary percutaneous coronary intervention. EPC samples were collected in 163 of 222 enrolled patients. At least one sample was obtained from 125 patients, and all three time points were available in 83 patients. There were no significant differences in the absolute EPC numbers over time or between EPO- and placebo-treated patients; however, there was a trend toward a greater increase in EPC levels from 24 to 48C72 h postintervention in patients receiving 30,000 U of EPO (P = 0.099 for CD133+ cells, 0.049 for CD34+ cells, 0.099 for ALDHbr cells). EPC numbers at baseline were inversely related to infarct size (P = 0.03 for CD133+ cells, 0.006 for CD34+ cells). Local whole cell cryopreservation and central EPC analysis in the context of a multicenter randomized trial is feasible but challenging. High-dose (30,000 U) EPO may mobilize EPCs at 48C72 h, and baseline EPC levels may be inversely associated with infarct size.